1. Field of the Invention materials and more particularly compounds The present invention is directed to the process and apparatus for the diffusion of semiconductor compounds to the diffusion of III-V semiconductor compounds in a semiclosed reusable tube.
2. Prior Art
According to prior techniques wafers of III-V semiconductor compounds such as GaAsP or GaP for use in fabricating light emitting diodes are diffused either by the closed tube method or an open tube method. In the case of closed tube diffusions both the dopant material and the wafers to be diffused are sealed with a dopant in an evacuated quartz ampoule which is then heated. This method has the advantage of yielding extremely uniform and reproducible results but has the disadvantage of requiring expensive and very time-consuming quartz work for each diffusion, together with the need to establish a very high vacuum.
There are two types of open tube diffusions. In one type the wafers are placed in an open tube and zinc as a dopant ffrom a from source is flowed down the tube. This diffusion is inexpensive and also hard to control for reproducible results and often results in surface damage, e.g., pitting. Moreover, a high flow rate is required to prevent oxygen from causing contamination and contributing to surface damage. In a second type of open tube diffusion the wafers are coated first with a densified oxide film and then with a zinc doped film and placed in an open furnace and diffused. The primary disadvantage of this technique is that the wafers must undergo the additional coating step and often do not exhibit uniform electrical properties.